This invention relates to radiographic imaging and more particularly to a system and method for obtaining real-time images of an object with very high space and time resolution.
In U.S. Pat. No. 5,850,425, an X-ray or neutron optic configuration includes a plurality of single crystal portions formed with respective spaced X-ray or neutron reflection faces formed at predetermined asymmetry angles to a Bragg diffraction plane in the respective crystal portion. The crystal portions are interconnected to maintain a first and second of these faces spaced apart for receipt of a sample between them and to allow small adjustments of the relative angle of the faces about the normal to the plane of diffraction while maintaining the normals to the Bragg planes for the first and second faces substantially in the plane of diffraction. A first face is arranged to be a monochromator and collimator with respect to X-rays or neutrons of appropriate wavelength incident reflected through the sample for receipt by the second face, which thereby serves as an analyzer face.
U.S. Pat. No. 5,850,425 also discloses a method of deriving an X-ray or neutron beam image signal of a sample comprising: directing an X-ray or neutron beam onto a first X-ray or neutron reflection face for reflection from that face through the sample to a second X-ray or neutron reflection face and thence to X-ray detection means, said reflection faces being interconnected such that a beam Bragg diffracted by the first face is at or near the correct angle of Bragg diffraction by the second face, said reflection faces being formed in respective single crystal portions at predetermined asymmetry angles to a Bragg diffraction plane in the respective crystal portion, wherein said first face is arranged to be a monochromator and collimator with respect to X-rays or neutrons of appropriate wavelength incident on said first face and reflected thereby through the sample for receipt by the second face said second face thereby serving as an analyzer face; and wherein the second face is well matched in angular acceptance to the angular divergence of the beam from the first face, or is of higher angular resolution.
The system of U.S. Pat. No. 5,850,425, includes a plurality of single crystal portions and means interconnecting the crystal portions located between the X-ray source and the detector. In order to convert a polychromatic beam into a monochromatic X-ray, the system has complicated single crystal portions and means interconnecting the crystal portions located between the X-ray source and the detector. Therefore, the system of U.S. Pat. No. 5,850,425 is very complicated, in particular in respect of a multiple reflection monochromator/collimator arrangement.
In the method of U.S. Pat. No. 5,850,425, since only a monochromatic beam extracted from the white beam is incident into an object, the flux of the beam passing through the object is a small amount and thereby the time necessary for imaging with X-rays is lengthened. Also, due to this reason, it is very difficult to obtain real-time images. Since the object of interests has to be exposed for a long time period in order to obtain an image with high resolution, the object is severely damaged.
On the other hand, in an other article, phase-contrast imaging using polychromatic hard X-rays, Nature 384: 335-338 (1996) by Wilkins S W, Gureyev T E, Gao D, Pogany A, Stevenson A W, a kind of optics pinhole is used. In this case, a polychromatic beam is used as an X-ray source. Since the pinhole is used as one element of the optics, the intensity of the X-rays is very low. For example, in the case that the distance between a specimen and a detector is more than 1 m, the exposure time is required to be about 60 minutes. Thereby there is a great limitation in obtaining high quality of real-time images. Also, when a sample such as live body is exposed for a long time, the sample is severely damaged.
U.S. Pat. No. 5,881,126 also discloses a phase-contrast X-ray imaging system comprising an X-ray interferometer, wherein X-ray interfering beams thicker than 2 cmxe2x96xa12 cm are formed enabling observation of comparatively large objects. The X-ray interferometer is constituted by two crystal blocks each of which is monolithically cut out from ingots of crystal and have two wafers which function as X-ray half mirrors. Optical equipment, a chamber, and a feedback system are incorporated to adjust and stabilize the crystal blocks. A device is also incorporated to obtain an image showing the distribution of the X-ray phase shift with which diagnosis becomes easier and reliable. In the optical system a monochromatic beam is used as an incident beam. The flux of the beam becomes extremely low and thereby it is not possible to obtain X-ray images with nearly real-time response.
It was thought in prior arts, for example Burattini E, Di Maggio C, Gambaccini M, Indovina P, Maryiani M, Porek M, Simeoni S, Simonetti G (1994) Mammogrphy with Synchrotron Radiation. Radiology 125: 239-244, that, in order to obtain images with high resolution, a monochromatic beam has to be used. In the case of biological imaging, enhanced contrasts, i.e., DPA (dual-photon absorptiometry) and KES (K-edge substraction) effects are achieved by the use of high atomic number (Z) contrast agents. Such agents would also typically lead to increase in magnitude of peak shifts associated with phase-contrast imaging since the real part of the refractive index is also essentially proportional to Z. However, as contrast agents are used, cumbersome processes are needed. Refer to Dilmanian F A, Wu X Y, Kress J, Ren B, Button T M, Chapman D, Coderre J A, Giron F, Greenberg D, Krus D J, Liang Z, Marcovici S, Parsons E, Petersen M J, Roque C T, Shleiger M, Slatkin D N, Thomlinson W C, Yamamoto K, Zhong Z (1997) Single and Dual-Energy CT with Monochromatic Synchrotron X-rays. Phys. Med. Biol. 42:371-387. Moreover, so as to obtain the monochromatic beam, an additional optical system is needed.
X-ray contact microscopy (Shinohara, Ito and Kinjo, 1994; Kinjo et al., 1994), imaging microscopy (Schmahl et al., 1991; Guttmann et al., 1992) and scanning microscopy (Kirz, 1991, Williams et al., 1992) have already been developed and applied to observe hydrated biological specimens. However, none of these microscopies are applicable to three-dimensional observation of thick hydrated biological specimens. Also, the quality of obtained images is not always sufficient for medical diagnosis.
It is one object of the invention to provide a system and a method for obtaining a real-time image of an object with high space resolution.
It is another object of the invention to provide a system and a method of imaging a diagnostic object at low dose levels.
The invention accordingly provides, in a first aspect, an imaging system comprising: a source for emitting a collimated white beam; means for filtering out photon energies lower than a selected energy level in the collimated white beam, thereby producing an unmonochromatized beam to be irradiated on an object; and means for detecting an unmonochromatized beam image having passed through the object. Preferably, the imaging system further comprises a processor for obtaining an image of the object based on an output of the detecting means. The collimated white beam emitting source includes a synchrotron radiation source.
The invention provides, in a second aspect, a method for imaging an object comprising: a step of extracting a collimated white (unmonochromatized) beam from a source; a step of filtering out the photon energies lower than a selected energy level in the collimated white beam, thereby producing an unmonochromatized beam; a step of irradiating the object with the unmonochromatized beam and a step of detecting an unmonochromatized beam image which has passed through the object. The collimated white beam is preferably but not exclusively from a synchrotron radiation source. This invention is effective in diagnostic applications with a reduced dose.